True, but only if the node does not use ADR or other downlinks. (For ABP, there is simply no joining phase as the “session” keys have already been programmed into the device, so no downlinks are needed to join the network. Once those keys are known, OTAA and ABP devices act the same for uplinks, downlinks, ADR, and so on, until an OTAA device somehow loses its keys and needs to join again.)
Hmmm, assuming we’re referring to gateways for TTN: I doubt that. If TTN thinks a gateway can do downlinks, I don’t think it’s going to use that only for “data” downlinks, and not for OTAA (or ADR, or other MAC commands)? Gateways just forward whatever the node or backend gives them; they don’t know if a downlink is some OTAA Join Accept or any other type of downlink.